Life history traits of the invader Dikerogammarus villosus (Crustacea: Amphipoda) in the Moselle River, France. Abstract The latest threatening invader in European freshwaters is Dikerogammarus villosus, a large gammarid of Ponto-Caspian origin exhibiting a predatory behaviour. Its biology and population dynamics were studied over a one-year period in a recipient ecosystem to determine bio/ecological traits having facilitated its rapid establishment. The study revealed that D. villosus reaches sexual maturity early, at six mm in length, and produces three reproductive peaks, though the species reproduces all year long, hence reflecting its multivoltine character. The study also revealed a female-biased sex ratio, exceptional growth rates of up to 2.6 mm in two-weeks in spring, and one of the highest fecundities of Western Europe gammarids. D. villosus exhibits a biological profile suggesting that only a few individuals can rapidly establish a new population in a recipient ecosystem, and allow this gammarid to become cosmopolitan in the near future.